1. Field of the Invention
The present invention relates to a magneto-optical disc recording apparatus, more particularly to a magneto-optical disc recording apparatus of the optical modulation type using magneto-optical (MO) discs.
2. Description of the Related Art
The known magneto-optical disc recording apparatuses are of the optical modulation type and the magnetic field modulation type. Magneto-optical disc recording apparatuses of the optical modulation type include ones which use magneto-optical disc recording media of the overwrite type and ones which use magneto-optical disc recording media of the non-overwrite type. Here, an illustration will be given of a magneto-optical disc recording apparatus of the optical modulation type using a magneto-optical disc recording medium of the non-overwrite type and making simultaneous use of both sides.
One known method for improving the rate of data transfer of magneto-optical disc recording apparatuses is to use the two sides of a single magneto-optical disc recording medium and to provide optical pickups and auxiliary magnetic field applying means at each of the two sides of that medium.
A magneto-optical disc recording apparatus which uses a magneto-optical disc recording medium of the non-overwrite type, however, cannot perform an overwrite operation, and so, for example, uses an erasure head to once erase data from the magneto-optical disc recording medium before recording data on the medium. Accordingly, basically, a minimum of two heads are required at the top and bottom sides. To enable data to be recorded on a magneto-optical disc recording medium in the same processing time as with a magneto-optical disc recording apparatus of the overwrite type in a magneto-optical disc recording apparatus of the non-overwrite type, however, it is necessary to provide a reproduction/recording head and a reproduction/erasure head at each side of the magneto-optical disc recording medium and therefore necessary to provide a total of four heads (four optical pickups) at the top and bottom sides of the magneto-optical disc recording medium.
These heads may be arranged by the method of placing them facing each other in the diametrical direction of the magneto-optical disc and the method of placing them apart by 90 degrees or another angle. In the following example, an explanation will be made of a magneto-optical disc recording apparatus of the type where the heads are positioned facing each other in the diametrical direction of the magneto-optical disc so there is freedom in mounting the optical pickups and the coarse motion motor for the tracking direction.
As such magneto-optical disc apparatuses, examples shown in FIGS. 1 to 3 can be considered.
FIG. 1 is a perspective view of a first example of the related art. It shows a magneto-optical driver (magneto-optical disc recording apparatus) having members arranged facing each other in the diametrical direction of the magneto-optical disc recording medium, that is, placed 180 degrees apart, and using medium (magneto-optical disc recording medium) of the non-overwrite type.
The magneto-optical disc recording medium 1 of the non-overwrite type is of the double-sided recording type. The magneto-optical disc recording medium 1 is affixed to a turntable of a rotational member 2 having a shaft and a turntable and is made to turn by a spindle motor 3 connected to the shaft of the rotational member 2.
The magneto-optical disc recording apparatus shown in FIG. 1 is provided with four optical pickups. Four heads are provided in these optical pickups. These four heads include a reproduction/recording head 4 for the top side of the magneto-optical disc recording medium 1, a reproduction/erasure head 5 for the top side provided in the same plane as the head 4 in the horizontal direction at a position facing it in the diametrical direction of the magneto-optical disc recording medium 1, a reproduction/recording head 6 for the bottom side of the magneto-optical disc recording media 1, and a reproduction/erasure head 7 for the bottom side provided in the same plane of the head 6 in the horizontal direction at a position facing it in the diametrical direction of the magneto-optical disc recording media 1.
Referring to the construction of the reproduction/erasure head 5 as a representative case, the heads 4 to 7 are slidable in the diametrical direction of the magneto-optical disc recording medium 1 by the bearings 8 and shafts 9 and moved by the coarse motion motors 10 to access specific positions in the track direction of the magneto-optical disc recording medium. The four optical pickups provided with the four heads 4 to 7, the sliding parts, and the coarse motion motors 10 are affixed to four bases 11. These four bases 11 are arranged on a sled base 12.
These four optical pickups are provided with auxiliary magnetic field application magnets which apply magnetic fields to the magneto-optical disc recording medium 1 at positions facing the heads across the magneto-optical disc recording medium 1. For example, for the reproduction/recording head 6 and the reproduction/erasure head 7, as illustrated, magnets 13 are arranged as the auxiliary magnetic field application magnets above the magneto-optical disc recording medium 1. The magnets for application of auxiliary magnetic fields to the reproduction/recording head 4 and reproduction/ erasure head 5 are not illustrated due to restrictions of the drawing, but are positioned at the reverse side of the magneto-optical disc medium 1 below those heads.
when recording data on the top side of the magneto-optical disc recording medium 1 in the magneto-optical disc recording apparatus using a magneto-optical disc recording medium 1 of the non-overwrite type of FIG. 1, the data at the portion to be recorded is erased by the reproduction/erasure head 5 and then data is recorded at the portion erased by the head 5 by the reproduction/recording head 4 facing it in the horizontal direction (diametrical direction of magneto-optical disc recording medium 1). When recording data at the bottom side of the magneto-optical disc recording media 1, the portion where the data is to be recorded is erased by the reproduction/erasure head 7 and then data is recorded at that portion by the reproduction/recording head 6.
When reproducing data from the top side of the magneto-optical disc recording media 1, the reproduction/recording head 4 and reproduction/erasure head 5 are used, while when reproducing data at the bottom side of the magneto-optical disc recording media 1, the reproduction/recording head 6 and reproduction/erasure head 7 are used.
Note that in the case of the magnetic field modulation type, there is no need to provide erasure heads corresponding to the reproduction/erasure heads 5 and 7 shown in FIG. 1, so the number of heads can be halved from the above.
In the magneto-optical disc recording apparatus shown in FIG. 1, there is a single magneto-optical disc recording media 1, but since an auxiliary magnetic field applying means has to be provided for each optical pickup, four auxiliary magnetic field applying means, for example, permanent magnets, are required for recording and reproducing data on a single magneto-optical disc recording media and thus there is the problem of a relatively larger number of permanent magnets.
The four optical pickups provided with the reproduction/recording head 4, the reproduction/erasure head 5, the reproduction/recording head 6, and the reproduction/erasure head 7 are disposed at 90 degree intervals along the circumference of the magneto-optical disc recording medium 1, so a base 11 for supporting an optical pickup is required every 90 degrees, that is, in each direction. Accordingly, the sled base 12 ends up becoming larger in both the width direction and the depth direction and it is difficult to reduce the size of the magneto-optical disc recording apparatus.
As a second example, an explanation will be made of the magneto-optical disc recording apparatus referring to FIG. 2.
As illustrated in FIG. 2, there is considered a magneto-optical disc recording apparatus in which the heads 14 and 15 provided at the optical pickups for the top side of the magneto-optical disc recording media 1 are arranged at the same positions as the heads 16 and 17 provided at the optical pickups for the bottom side, respectively, except facing each other across the magneto-optical disc recording medium 1 in the vertical direction, that is, the head 14 faces the head 17 and the head 15 faces the head 16 at same positions across the magneto-optical disc medium 1 in the vertical direction.
In this example, the basic configuration of the magneto-optical disc recording apparatus is the same as that in FIG. 1. Only the positions of the optical systems are different. That is, the magneto-optical disc recording apparatus shown in FIG. 2 has, in addition to the magneto-optical disc recording medium 1, the rotational member 2 having the shaft and turntable, the bases 11, the sled base 12, etc., a spindle motor, bearings, shaft, coarse motion motors, auxiliary magnetic field application magnets, etc. in the same way as in FIG. 1, though not shown in FIG. 2.
In this magneto-optical disc recording apparatus, the portion where the data is to be recorded is erased by the top side optical pickup reproduction/erasure head 15, then data is written by the top side optical pickup reproduction/recording head 14 at the portion where the data was erased. In the same way, the portion where the data is to be recorded is erased by the bottom side reproduction/erasure head 17 and then data is written at the portion where the data was erased by the bottom side reproduction/recording head 16.
In this example, a plurality of auxiliary magnetic field application magnets must be provided in the respective heads 14 to 17. Such optical pickups, each functioning as both the auxiliary magnetic field application means and the optical system, can be realized by a method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 4-332940, however, the construction of that magneto-optical disc recording apparatus ends up becoming complicated.
A third example will be explained referring to FIG. 3.
As illustrated in FIG. 3, another method for improving the rate of data transfer of a magneto-optical disc recording apparatus is to divide the magneto-optical disc recording medium 1 into an inner circumference area and an outer circumference area which are used independently and to make simultaneous use of a total of four top pickups and four bottom pickups. That is, a total of four heads are provided at the top side: the inner circumference reproduction/recording head 18, the inner circumference reproduction/erasure head 19, the outer circumference reproduction/recording head 20, and the outer circumference reproduction/erasure head 21. The same types of heads as the top side are provided at the bottom side of the magneto-optical disc recording medium 1 as well. Therefore, a total of eight optical pickups are mounted at the two sides. The auxiliary magnetic field application magnets are provided at locations facing these optical pickups across the magneto-optical disc recording medium 1.
In this example as well, in the same way as explained with reference to the magneto-optical disc recording apparatus of FIG. 2, the basic construction of the magneto-optical disc recording apparatus is the same as the magneto-optical disc recording apparatus shown in FIG. 1 with just the deployment of the optical systems being different.
In this magneto-optical disc recording apparatus, when recording data at the outer circumference area on the top side of the magneto-optical disc recording medium 1, the data of the portion to be recorded on is erased by the outer circumference reproduction/erasure head 21 and then data is written at the portion where the data was erased by the outer circumference reproduction/recording head 20. When recording data at the inner circumference portion of the top side of the magneto-optical disc recording medium 1, the portion where the data is to be recorded is erased by the inner circumference reproduction/erasure head 19 and then data is written on the portion where the data was erased by the inner circumference reproduction/recording head 18. Data is recorded on the outer circumference and inner circumference areas of the bottom side of the magneto-optical disc recording media 1 in the same way as the above.
The magneto-optical disc recording apparatus shown in FIG. 3 requires the provision, at the top side of the magneto-optical disc recording medium 1, of the inner circumference reproduction/recording head 18, the inner circumference reproduction/erasure head 19, the outer circumference reproduction/recording head 20, and the outer circumference reproduction/erasure head 21, or a total of four heads (or optical pickups), while requires the provision of four heads at the bottom side as well in the same way as above, so eight optical pickups had to be provided above and below for the two sides.
In a case where separate auxiliary magnetic field applying means and optical systems are required such as in the case of the magneto-optical disc recording apparatus shown in FIG. 1, it is not possible to arrange the optical pickups at 90 degree intervals from each other. There were great restrictions in dimensions in terms of structure and therefore the apparatus was difficult to realize.